Stephen Miller, a senior policy adviser to Trump's GOP presidential campaign and a former top aide to Alabama Sen. Jeff Sessions, made the claim on CNN's "State of the Union" Sunday.

"You want to talk about women's issues? Here's something we should be talking about. It is a fact: As a result of uncontrolled migration into this country -- you can look this up, it's a statistic from Equality Now -- half a million U.S. girls in this country are at risk of female genital mutilation," Miller said.

Neera Tanden, the president of the Center for American Progress, shot back that his comment was an example of Trump backers' tactic of saying "something outrageous."

He cited a report issued by the Centers for Disease Control and Prevention in January that said 513,000 women and girls in the United States are considered at-risk because they were either born themselves or have a parent born in a country where female cutting is a tradition.

Miller highlighted Equality Now, an organization that fights to end female genital mutilation.

He pointed CNN's "State of the Union" host Jake Tapper to a Reuters article in January that highlighted the findings.

Asked whether the Trump campaign stands by Miller's remarks, Trump spokeswoman Hope Hicks responded only by sending a link to a Newsweek article that highlighted similar findings. That article, though, pointed out that the figure is strictly the result of increased migration from African and Middle Eastern countries -- and that there's no evidence of the practice increasing in the United States.

Miller's comment came during a discussion of Trump's Twitter attacks on Heidi Cruz, the wife of Texas Sen. Ted Cruz, one of Trump's GOP presidential opponents. Miller dismissed that controversy as media-driven and said more important issues like immigration deserve attention instead.